Fibronectin (opsonic protein) concentrated in human plasma cryoprecipitate has been shown by others to be effective in the treatment of septic shock. Should this protein be further demonstrated to be useful as a therapeutic agent, large amounts will be required for clinical testing and treatment. Therefore, alternate sources to blood banking procedures are desirable to be explored. The overall goal of the proposed research is to utilize microcarrier-grown human cell cultures, especially fibroblasts, for the production and subsequent bioaffinity purification of fibronectin. The investigation involves screening a number of human fibroblast lines and other cells for their ability to produce fibronectin, exploring the influence of cell age and cell cycle in this process and optimization of environmental conditions (e.g. micro-carrier density, bead charge, nutrients, etc.) to obtain the maximum yield of protein. The proteins will be tested for opsonic activity in vitro and for possible therapeutic effectiveness in experimental animal models. Fibronectin produced by cell cultures may be used advantageously from economic and safety considerations over plasma cryo-precipitate infusion.